Fig. 1. (a) Spiral phase of optical vortices; (b) A spiral phase plate; (c) A fork-shaped diffraction grating

Fig. 2. (a) Vortex generator composed of nano units with different sizes and interference patterns; (b) SEM image of the silicon metasurface and reconstructed phase of the beam of object surface

Fig. 3. Schematic of the spin-orbit coupling through a plasmonic metasurface (Inset: interference pattern of the generated vortex beams with planar or spherical waves^[71])

Fig. 4. (a) Phase profile of the metasurface and corresponding scanning electron microscope image; (b) Intensity and (c) interference pattern of the transmitted field^[72]

Fig. 5. (a) Phase control ability of V-shaped optical nantennas^[35]; (b) Metasurface vortex generator composed of 8 V-shaped nantennas and the interference patterns^[35]; (c) Phase shift and amplitude in cross polarization of 3 group V-shaped antennas; (d) High-order vortex generator composed of V-shaped nantennas^[73]

Fig. 6. (a) Schematic of the arbitrary spin-to-orbital angular momentum conversion^[74]; (b) Schematic of the structure and function of periodic-rings metasurface^[75]; (c) Phase distribution, SEM image and generated optical vortices of a metasurface fork-shaped grating^[78]

Fig. 7. (a) Schematic and phase coding of vortex generator^[92]; (b) Schematic of a metasurface hologram^[93]; (c) Structure, SEM image and phase of the hologram metasurface vortex generator^[94]

Fig. 8. (a) Schematic of metasurface units and the generation of multiple vortex beams^[96]; (b) Schematic of OAM-based free-space optical communications using the Dammann optical vortex grating for multiplexing/demultiplexing^[98]

Fig. 9. (a) Shared-aperture phased antenna array. Far-field intensity distribution of segmented, interleaved, and harmonic-response metasurfaces^[101]; (b) Intensity distribution and interference pattern of segmented vortex generator^[102]; (c) SEM image of the metasurface and experimental results of multichannel interleaved phase^[103]; (d) Generation and reconstruction of the 3D vortex array based on a dielectric metasurface^[107]